1. Field of the Invention
The present invention relates to a ball joint device for use in a joint of steering or suspension systems of automobiles, and more particularly to a ball joint of automobiles which removes the damage caused by twist occurring in the assembly process.
2. Description of Related Art
Various types of ball joints for use in a vehicle are well known in the art. A ball joint rotatably and tiltable on any plane surface is generally used for a steering or a suspension system of automobiles. A conventional ball joint has a structure in which a spherical head of a ball stud is inserted into the inside of a ball seat under the condition that its rotational and tilt operation is enabled; the ball seat is fixed to a housing and a dust cover is fixed between the cross portion of a housing and a ball seat.
FIGS. 1 and 4 show an existing ball joint disclosed in Japanese Laid-Open Patent No. Hei 1-172610. A ball seat 102 where a spherical head 101a of a ball stud 101 movably inserted is installed in a housing 103. And then a combining plate 102a provided at the closed portion of the ball seat 102 is heated to be bent outwardly so that the combining plate 102a is hook-combined with the lower portion of the housing 103. That is, one plate of a dust cover 104 is fixed by a rib 105 at a groove formed between a hook protrusion 102b of the ball seat 102 and a step of the housing 103.
In such a ball joint, the combining plate 102a provided at the lower portion of the ball seat 102 is heated and melted to be bent to the outward of the lower portion of the housing 103, thus being hook-combined.
To prevent the ball seat 102 inserted into the housing 103 from rotating while in operation, a V-shaped fixing groove (not shown) is provided at the step of the housing 103 where the combining plate 102a of the ball seat 102 is hook-combined with the housing 103, and melted by heating. Thus, the rotation of the combining plate 102a of the ball seat 102 is prevented.
However, such a ball joint must be additionally provided with the V-shaped fixing groove, and the combining plate 102a must be heated during a manufacturing process adding difficulty and cost to the process. The combining strength between the ball seat 102 and the housing 103 is increased when the thickness of the combining plate 102a formed on the ball seat 102 is thickened. However, when the combining plate 102a is thickened, it is more difficult to melt.
As shown in FIGS. 2 and 4, a ball joint in which a housing 103 where a support formed of a metallic material is welded is provided. After the ball seat 102 formed of a plastic material (including the spherical head 101a of the ball stud 101) is inserted into the housing 103, a covering cap 106 formed of a plastic material is welded to the lower portion of the ball seat 102 by an ultrasonic vibrator. While welding protrusions 106a formed on the covering cap 106 are melted and welded, the ball seat 102 is fixed to the housing 103. Such a ball joint is disclosed in U.S. Pat. No. 5,011,321 to Kidokoro.
However, the method in which that the ball seat 102 is fixed to the housing 103 by welding a covering cap 106 to the ball seat 102 requires additional equipment, and further, requires an apparatus for verifying the welding state. Though the verification apparatus is employed, it is not easy to verify the state of weldment of the covering cap 106 onto the ball seat 102 with accuracy.
FIGS. 3 and 4, disclose and alternative ball joint. An outwardly bent annular hook protrusion 102c is made at the closing portion of a ball seat 102 where a spherical head 101a of a ball stud 101 is inserted. An annular hook protrusion 102c is hooked and fixed at the lower portion of a housing 103, and thus the ball seat 102 is fixed to the housing 103. The diameter of the annular hook protrusion 102c formed at the closing portion of the ball seat 102 is formed to be greater than that of the ball seat 102. Such a ball joint is disclosed in Japanese Utility Laid-Open Patent No. Hei 5-23852.
However, in such a ball joint, the annular hook protrusion 102c may become damaged when a ball seat 102 is inserted in a housing 103, and a combining strength of an annular hook protrusion 102c of the ball seat 102 being hooked and fixed to the housing 103 is weak.
That is, the ball seat 102 is generally inserted by using a tool. Accordingly, when the ball seat 102 does not uniformly receive force from the tool for inserting the ball seat 102 into a housing 103, the ball seat 102 is twisted. Also, when a twisted ball seat 102 is assembled into the housing 103, an annular hook protrusion 102c is easily broken since the diameter of the annular hook protrusion 102c is formed to be greater than that of the ball seat 102. When the ball seat 102 slips out of the housing 103 by a vertical force of a ball stud 101 during operation of the ball joint, the annular hook protrusion 102c cannot withstand the force and is damaged.
FIGS. 5 and 6 illustrate another existing ball joint. The first hook protrusion 112a and the second hook protrusion 112b are formed at the open portion of a ball seat 112 and a dust cover 104 is fixed by a rib at a fixing groove 112c formed between the first hook protrusion 112a and the second hook protrusion 112b. This configuration avoids the likelihood that the dust cover 104 will receive much stress by the operation of a ball joint, such as by shaking and rotating, and makes assembly process automation possible by inserting a ball seat 112 into a housing 113 and fixing it, then fixing a dust cover 104. Such a ball joint is disclosed in U.S. Pat. No. 5,676,485 to Lee.
In order to solve problems such as when a ball seat 112 turns inside a housing during the operation of a ball joint and the ball seat 112 gets twisted and damaged by a tool when the ball seat 112 is inserted into the housing 113, the inside of the housing 113 and the outer body of the ball seat 112 have the same polygonal shape and several incised plates are formed at an annular hook sill 112d formed on the ball seat 112.
In addition, to fix a ball seat 112 in a housing 113 and maintain the fixing strength, a cap 114 is placed on an annular hook sill 112d formed at the lower closing portion of the ball seat 1122. However, the ball joint above has the problem that it can't be easily assembled by an automated process because a ball seat 112 must be inserted into a housing 113 with their polygonal angle being conformed.